Method, computer program and printing system for trapping of print data

ABSTRACT

In a method, a printing system and a computer program for trapping of print data with a plurality of objects, the print data are generated, prepared and/or transferred together with trapping instructions in a print data stream for execution of the trapping. The print data stream references resource data that comprise trapping parameters and/or trapping instructions. The method can be executed in real time without a delay in the printing process hereby occurring. It can therefore be integrated into a print data stream for electrographic high-capacity printers.

BACKGROUND

The preferred embodiment concerns a method, a computer program and aprinting system for trapping of print data.

The preferred embodiment is connected with other disclosures that aredescribed in the German patent applications DE 10 2006 055 587.2, DE 102006 055 624.0, DE 10 2006 055 625.9 and DE 10 2006 055 626.7. Theircontent is herewith incorporated by reference into the presentspecification.

Color documents or document parts such as, for example, images, colorgraphics or the like are for the most part described by image data thatare subdivided into color separations. This type of the data division inturn corresponds to many print output methods or apparatuses that printthe image data in color separations on a recording medium, for examplein the colors yellow (Y), magenta (M), cyan (C) and black (K) or inblack and one or more colors, what are known as highlight color colorsor the Océ Custom Tone® colors.

The application develops and distributes corresponding digitalelectrographic printing systems. For example, they are described in thepublication “The World of Printers, Technologies of Océ PrintingSystems”, Dr. Gerd Goldmann (Editor), Océ Printing Systems GmbH, Poing,7th Ed. (2002). Various offset and digital printing technologies aredescribed on pages 249-286, various digital color printing system aredescribed on pages 287-325 and foundations of color printing aredescribed on pages 233-248. Bases of digital image processing aredescribed on pages 209-232. Principles of highlight color printing aredescribed on pages 246-248.

A digital printing system for two-sided monochrome and/or color printingof a recording medium is known from WO 98/39691 A1. A method forpreparation of a pixel file in which contiguous areas of the image thatare made up of the pixels are determined is known from the internationalpatent application Nr. PCT/EP2004/00700 (publication number WO2005/001765).

Methods for trapping of image data are known from U.S. Pat. No.5,581,667, EP-A2-484 890, US 2003/0090689 A1 as well as US 2006/0033959A1, U.S. Pat. No. 4,931,861, EP-A2-929 189, DE-A1-199 12 511, US2001/0055130 A1 and EP-A2-833 216.

There is what is known as the passer problem in both digital printingand offset printing. It is thereby that, given a plurality of printingprocedures on one sheet of paper, due to mechanical tolerances it cannotbe guaranteed that the positioning of the paper is always exactly thesame in all printing procedures. The problem occurs in single-colorprinting when front side and back side are printed separately or givenmulti-color printing on one side.

Given front and back side printing this problem occurs when, forexample, a border is printed on each of the front and back sides andthese borders do not exactly lie atop one another, which is noticed whenthe page is held up to the light.

Given multi-color printing the colors are offset relative to oneanother. As long as the different colors do not touch, this does notstand out further. If the colors touch, due to the offset, the colorsare printed atop one another at the contact line, which leads to anadulteration of the color impression or a white gap (flash) at thecontact line.

While the adulteration of the color impression is for the most partstill tolerable, the flashes are extremely noticeable, as is shown bythe comparison of exactly positioned colors in FIG. 1A and offsetpositioned colors in FIG. 1B.

To remedy the flash problem it is known to enlarge or, respectively, tospatially over-fill the lighter colors. Although a greater overlap ofthe colors is therewith obtained, the flashes disappear, as is shown bythe comparison of offset positioned colors in FIG. 2A and overlappedcolors in FIG. 2B. Given the enlargement of an object care must be takenin the later printing procedure that the overlapping part is printedtranslucent since otherwise the problem shifts to the edge of theenlarged object.

The method just described that remedies this problem has the name“trapping” (overfilling). Trapping is offered in different products onthe market. For example, it is a component of raster image processors(RIPs) of the page description language (PDL) Adobe PostScript Level 3,the software SuperTrap® offered by the company HeidelbergerDruckmaschinen AG or the software TrapWise® that is offered by thecompany Creo.

Trapping can be implemented in two different ways. Trapping can be dealtwith at the object level or at the bitmap level.

In electrophotographic high-capacity printing systems the problem oftrapping was previously solved at the bitmap level (see, for example, WO2006/069980 A1), since at the bitmap level the print data can beautomatically processed without delay. Corresponding trapping methodscan therefore be integrated into an electrophotographic high-capacityprinting system without the printing operation hereby being impaired.

However, given the treatment of trapping at the bitmap level theinformation regarding the objects is missing, whereby the trapping atthe bitmap level is in principle significantly less efficient than thetrapping at the object level.

The products indicated above that are available on the market (which arecomponents of raster image processors (RIPs) of the page descriptionlanguage (PDL) Adobe PostScript Level 3, the software SuperTrap® offeredby the company Heidelberger Druckmaschinen AG or the software TrapWise®that is offered by the company Creo) generate additional trappingobjects at the borders of the objects, which trapping objects reduce theeffect of the passer problems. These additional trapping objectssignificantly increase the data volumes of the corresponding print datafile. In extreme cases the data volume can even increase tenfold sincethe number of the individual objects can be multiplied. Given theseknown solutions the trapping is executed interactively so that anexperienced user efficiently controls the generation of the additionaltrap objects dependent on the document to be trapped. These methods haveproven their worth in offset printing, in which a great deal of time isnormally available in order to correspondingly process the printdocument and interactively implement a trapping before the printingprocedure.

A method in which a trapping is executed in an electrophotographicprinter is known from US 2003/017934 A1. In this method edge lists areproduced from the objects and objects that do not correspond to apredetermined shape are divided up into corresponding standard shapes.Information of the objects is thus stored with the edge lists beforethey are rastered. The trapping itself occurs at the bitmap level,whereby the additional information of the objects (for example in theform of the edge lists) is taken into account as well. The disadvantageof the trapping on the bitmap level, that information regarding theobjects is no longer present, is thus somewhat reduced with this method.However, the generation of these edge lists is on the one handcomplicated and additionally a plurality of objects are generated fromindividual objects, which again makes the processing more difficult.Furthermore, the objects so generated are no longer identical with theoriginal objects. Objects with complex shapes cannot be processed or canonly be processed in a very limited manner with this method.

A method for trapping of print data present in a print page language(PDL—Page Description Language) arises from U.S. Pat. No. 5,666,543. Theprint data are hereby initially analyzed and trapping instructions aregenerated before said print data are supplied to a raster imageprocessor (RIP). The trapping instructions indicate whether the printdata comprise text or graphics and whether they should be trapped in theRIP using a shape directory. The shape directory is generated in theanalysis of the print data and transmitted to the RIP. The shapedirectory is a list of the shapes of the objects. The trapping regionsor overfills are generated upon rastering in the RIP. This known methodcorresponds to the method known from US 2003/017934 A1, whereby theshape directory corresponds to the edge list.

The prior art can thus be summarized to the effect that there aretrapping methods on the one hand that trap at the object level. However,these methods are not suited to implement the trapping in real timeduring the printing procedure in a digital electronic printing machine.These methods are primarily provided for offset printing in which theimage data are processed with an external raster image processor. On theother hand, it is known to implement trapping in real time in digitalelectronic printers. However, here the trapping occurs at the bitmaplevel, whereby limited information regarding the objects is madeavailable to the trapping on the bitmap level by means of edge lists orshape directories.

It was previously assumed that trapping at the object level in a digitalprinting machine cannot be implemented in real time since a user cannotinteractively affect the trapping with regard to the plurality ofdifferent rules and the trapping at the object level requires suchlarge-volume files that cannot be processed in real time.

Electrophotographic high-capacity printing systems are often componentsof digital production printing environments in which the pre- andpost-processing of printed media is executed in an automaticallycontrolled manner. In such production environments the document data aretransmitted between the individual workstations in the form of documentdata streams.

Various print data streams and printing systems that are suitable forprocessing of the most varied print data streams (including AFP andIPDS) are described in the already aforementioned publication “The Worldof Printers, Technologies of Océ Printing Systems”, Dr. Gerd Goldmann(Editor), Océ Printing Systems GmbH, Point, 7th Ed. (2002), ISBN3-00-001019-X. In chapter 13 (pages 343 through 361) the print serversystem Océ PRISMAproduction is described in this regard, for example.This flexible print data server system is, for example, suitable toconvert print data from data sources (such as a source computer) into aspecific output format (the print data to be received in a specificprinter data language such as AFP (Advanced Function Presentation),MO:DCA, PCL (Printer Command Language), PostScript, SPDS (Siemens PrintData Stream), in the Portable Document Format (PDF) developed by thecompany Adobe Systems Inc. or in the language Line Coded Document DataStream (LCDS) developed by the company Xerox Corporation) into aspecific output format (for example into the Intelligent Printer DataStream (IPDS) format) and to transfer the data to a print productionsystem in this uniform output format. Various technologies for colorprinting are described in chapter 10.

In the specification and further development of print data streams theproblem sometimes exists that new commands must be inserted into thedata stream in order to allow for the further technical developments ofcomputers, printing apparatuses and/or post-processing apparatuses. Theestablishment of such extensions is for the most part a relativelycomplicated method in which various industry partners must cooperate inorder to match the changes or, respectively, innovations among oneanother.

In U.S. Pat. No. 6,097,498 it is described how three new data streamcommands (namely WOCC, WOC and END) are to be added to the IntelligentPrinter Data Stream (IPDS™).

A further possibility to store additional control data in an AFP datastream is to store data in what are known as object containers (see, forexample, the pages 93-95) in the publication Nr. SC31-6802-05.

Further techniques for insertion of new control information into AFP orIPDS data streams are described in WO 03/069548 (originating from theapplicant).

How data objects such as text, images, graphics, barcodes and fonts arehandled in the data streams AFP and IPDS is described in the IBMpublication SC31-6805-05 with the title “Image Object ArchitectureReference”. For this what is known as an Object Content Architecture(OCA) is defined in which data structures designated for the respectiveobjects and control parameters or parameters identifying the objects areestablished; for example, what is known as the Image Object ContentArchitecture (IOCA) for images, a corresponding GOCA for graphics, aPTOCA for presentation texts etc. The IOCA is described in detail in theaforementioned document. Further IBM documents that are helpful for theunderstanding of the data streams are cited on pages v through vii ofthe document.

Details of the document data stream AFP™ are described in thepublication Nr. F-544-3884-01, published by the company InternationalBusiness Machines Corp. (IBM) with the title “AFP Programming Guide andLine Data Reference”. The document data stream AFP was further developedinto the document data stream MO:DCA™ which, for example, is describedin the IBM publication SC31-6802-06 (January 2004) with the title “MixedObject Document Content Architecture Reference”. Details of this datastream are also described in U.S. Pat. No. 5,768,488. Specific fielddefinitions of the data stream that contain control data (what are knownas “structures fields”) are also explained there.

AFP/MO:DCA data streams are frequently converted into data streams ofthe Intelligent Printer Data Stream™ (IPDS™) in the course of printproduction jobs. Such a process is shown in U.S. Pat. No. 5,982,997.Details regarding IPDS data streams are, for example, described in theIBM document Nr. S544-3417-06, “Intelligent Printer Data StreamReference”, 7th edition (November 2002).

IPDS and AFP data streams normally contain and/or reference what areknown as resources that contain data that are required for output of thedocuments. Via simple referencing, the data of a resource can thereby beused multiple times for one or more print jobs (that in turn comprise aplurality of documents or, respectively, document parts) without havingto be transferred multiple times. The quantity of the data to betransferred from one processing unit (for example a host computergenerating the documents) to a subsequent processing unit (for example aprint server or a printing apparatus) is thereby reduced, in particularwhen data from a plurality of documents that comprise or require thesame data in part are to be transferred. Examples of such resources arecharacter sets (fonts) or forms to be overlaid with documents(overlays). The resources can thereby be contained in the print datastream itself or be transferred separately from this between theparticipating systems and only be respectively referenced within variousdocuments. It can in particular be provided that the resources arealready stored in the further processing apparatus (for example printserver or printing apparatus), such that they do not have to bere-transferred with each print job but rather only must be referenced.

Given the presentation of AFP document data, resources that are situatedat various points in the AFP document data stream or originate fromvarious sources are merged with the corresponding variable data. Theresource data can thereby be integrated into the document data stream asinternal resources or be retrieved from libraries as external resourcesvia a resource name. Furthermore, the data are checked for consistencyin a parsing process.

In the document “Print Services Facility for OS/390 & z/OS,Introduction”, Version 3, Release 3.0, Nr. G544-5625-03 by the companyIBM from March 2002, details are described of how what is known as aline data or MO:DCA document data stream is converted into anIntelligent Printer Data Stream data stream. The software program PrintService Facility (PSF) thereby combines variable document data withresource data into output data that are sent to a printer (as an outputapparatus) to administer and control said printer. Software productsunder the trade name Océ SPS and Océ CIS that exhibit correspondingfunctions are developed and distributed by the applicant.

A method for secure administration and allocation of resources in theprocessing of resource-based print jobs is known from US 2005/0024668A1. A method for processing of resource data in a document data streamis known from WO-A1-2004/0008379.

Methods for color reproduction in offset printing machines are knownfrom Stollnitz, J. et al., “Reproducing Color Images Using Custom Inks”,ACM Proceedings of the 25^(th) annual conference on Computer graphicsand interactive techniques, SIGGRAPH '98, ACM Press, July 1998.

The further aforementioned publications or documents and patentapplications are herewith incorporated by reference into the presentspecification, and the methods, systems and measures described there canbe applied in connection with the present preferred embodiment.

SUMMARY

It is an object to achieve a method, a computer program and a system fortrapping of print data, whereby the trapping can largely be executedautomatically. The trapping can in particular be executable in anelectronic, digital high-capacity printing system.

In a method for trapping of generated print data with a plurality ofobjects, generating the print data together with trapping instructionsin a print data stream for execution of the trapping. The print datastream is transferred to a print data processing apparatus. With theprint data stream referencing source data that comprise at least one oftrapping parameters or the trapping instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a through 1 c schematically illustrate the insertion of anobject into a bitmap file;

FIGS. 2 a through 2 c schematically illustrate the insertion of anobject into a bitmap file;

FIG. 3 schematically illustrates a printing system in a block diagram;

FIG. 4 shows the fundamental workflow of the method of the preferredembodiment in a flow chart;

FIG. 5 illustrates the insertion of an object into the bitmap file in aflow chart;

FIG. 6 shows tables of individual trapping parameters;

FIGS. 7 a and 7 b illustrate an overfill in the region of a point of anobject;

FIGS. 8 a and 8 b show an overfill in the region of a boundary line withbrightnesses varying along the boundary line;

FIG. 9 schematically illustrates, an example for a hierarchicalstructure of an IPDS print data stream; and

FIGS. 10, 11, 12 show trapping examples in a print data stream.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the preferred embodiment/bestmode illustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, and such alterationsand further modifications in the illustrated device and such furtherapplications of the principles of the invention as illustrated as wouldnormally occur to one skilled in the art to which the invention relatesare included.

In a first aspect of the preferred embodiment, for trapping of printdata with a plurality of objects the objects are individually carriedover into a pixel file and the following steps are respectivelyexecuted:

-   -   determination, according to predetermined trapping rules, of at        least one overfill for the respective object relative to the        color regions adjoining the object in the pixel file and    -   insertion of the object and the at least one overfill into the        pixel file, whereby upon insertion the object and the overfill        are rastered in the pixel file.

Via the transfer of individual objects the advantage can be achievedthat the entire information of the objects is available for thecalculation of the overfills without the production of additional tablesor lists about the shape of the objects. Since the overfills in thepixel file are then immediately generated either given knock-out orgiven rastering, it is not necessary to generate additional objects atthe object level for the overfills. The determination of the overfillsusing the individual objects with regard to the pixel file and theinsertion of the overfills into the pixel file can thus be executed inthe print data controller of the printing apparatus without delay of theprinting process.

The transfer of individual objects does not necessarily mean that only asingle object can be carried over at a specific point in time. It isalso possible that a plurality of objects are carried over in parallelfrom the print data into the pixel file. Rather, individually means thatthe objects that are carried over do not spatially overlap in the imagewith other objects that are simultaneously transferred (such that thecalculation of the overfills would hereby be significantly complicated).

The overfills are generated both upon knock-out via reduction of thearea for the objects to be inserted and upon rastering via expansion ofthe objects with overfills.

Since the objects are individually transferred into the pixel file, thetrapping can be executed in a print server and/or printing apparatuswithout delay of the printing process. It is thus possible to trap aprint data stream “on the fly”.

The method is advantageously implemented in real time in a print datacontroller of a printing apparatus.

In a second aspect of the present preferred embodiment that can beapplied alone or in connection with the first aspect, a method isprovided for trapping of print data with a plurality of objects, inwhich method overfills are determined only at edges of one of therespective objects when the brightness of the respective object differsfrom the adjoining region by a difference amount that is greater thanthe predetermined threshold. Given adjoining objects with similarbrightness, it is hereby possible to provide no overfills since thesebarely appear due to the similar brightnesses. The calculation of asignificant number of overfills is thereby foregone, whereby it issimpler to implement the inventive method in real time. This method isadvantageously developed such that overfills are always determined givenan object with highlight color color even if the adjacent object shouldpossess a similar brightness, since given an incorrect registration ofan object comprising a highlight color color what are known as the“flashes” (which are narrow white gaps between adjoining objects thatshould be avoided) always arise.

In a third aspect of the present preferred embodiment that can beapplied alone or in connection with the aforementioned aspects,overfills in the region of a narrow, long point that, for instance, forma corresponding point are not extended beyond a predetermined width ofthe overfill in the X-direction and in the Y-direction relative to theoutermost point of the point of the non-trapped object. According tothis aspect of the invention, the overfill can simply be truncated whena specific distance from the point is reached. This method can beimplemented with the least computational effort. The execution of theinventive method in real time and without elaborate computer devices ishereby made easier.

According to a fourth aspect of the present preferred embodiment thatcan be applied alone or in connection with the aforementioned aspects, amethod for trapping of print data with a plurality of objects isprovided. The print data are thereby generated together with trappinginstructions in a print data stream for execution of the trapping,transferred to a print data processing apparatus and/or processed in aprint data processing apparatus, whereby the print data streamreferences resource data that comprise trapping parameters and/ortrapping instructions.

The print data stream can in particular be transferred to a print dataprocessing apparatus, for example to a printing apparatus. The trappingparameters and/or trapping instructions are advantageously comprised ina print data protocol.

A method for trapping of print data with a plurality of objects can alsobe provided in which print data together with trapping instructions aretransferred in a print data stream for execution of the trapping in aprinting apparatus. The trapping instructions can in particular becomprised in a print data protocol. The print data stream therebyreferences resource data that comprise trapping parameters and/ortrapping instructions.

The use of the resource structure for the trapping is in particularparticularly advantageous when an operator of a printing system adjustsin a print data processing apparatus such as, for example, a printserver, a raster processor a print data controller (arranged forexample, in a printing apparatus) via storage of corresponding trappingresources. The adjustment of this apparatus can thereby advantageouslyoccur individually in a specific trapping method. Furthermore, for eachprint job it can thereby advantageously be that the trapping parametersand/or trapping instructions are not to be re-transmitted to theapparatus executing the trapping.

The fourth aspect of the preferred embodiment can thereby in particularalso include the generation and administration of correspondingtrapping. These can, for example, be generated and modified as a file orfile collection (library) in a host computer, a client or a printserver, be administered in these computers and be stored and exchangedbetween them. They can also be exchanged with a printing apparatus witha data stream or independent of a data stream, in particular betransferred to it or be received by it, be stored, generated, modifiedor administered in said printing apparatus.

According to a fifth aspect of the preferred embodiment that can beapplied alone or in connection with the aforementioned aspects, it isprovided that for trapping of print data the print data are generated,prepared and/or transferred in a print data stream together withtrapping instructions. The print data stream is thereby structured indifferent levels and the trapping instructions comprise level-relatedpriority rules. The print data stream can in particular be transferredto a print data processing apparatus. It can be transferred to aprinting apparatus.

According to a sixth aspect of the preferred embodiment that can beapplied alone or in connection with the aforementioned aspects and inparticular in connection with the fifth aspect, for trapping of printdata the print data in a print data stream are generated, transferredand/or processed in a print data processing apparatus together with thetrapping instructions. The print data stream is structured in differentlevels. The higher the level, the greater its scope in which theinstructions contained in the respective levels act. According to thisaspect of the invention, trapping instructions from lower levels havepriority relative to trapping instructions from higher levels.Corresponding to this, a priority instruction can in particular beprovided according to the fifth aspect. The print data stream can inparticular be transferred to a print data printer or copier apparatus.It can be transferred to a printing apparatus.

Printing instructions (in particular color instructions) are typicallyinherited from higher levels to lower levels. This means that a printinginstruction in a higher level automatically affects all levels situatedbelow it. The printing instructions in higher levels thus typically havepriority over printing instructions in lower levels.

Contrarily, given trapping it is advantageous when the trappinginstructions from lower or bottom levels have priority over trappinginstructions of higher levels since the trapping instructions in a lowerlevel are directly related to the respective object and thus are morespecific to the respective object.

According to a seventh aspect of the preferred embodiment that can beapplied alone or in connection with the aforementioned aspects, and inparticular with the fifth aspect, the print data in a print data streamare transferred together with trapping instructions into a printingapparatus and the print data stream is structured in different levels.The higher the level, the greater the scope in which the instructionscontained in the respective level act. According to this aspect, atrapping instruction is provided in the highest level, with whichtrapping instruction the trapping can be activated or deactivated in theentire range of the highest level. This in particular represents a typeof global switch with which trapping can generally be activated ordeactivated. In principle, the possibility is hereby granted to theoperator of a printing system to activate or deactivate trapping in aprint data stream when the respective trapping instruction isrespectively [sic] used alone in the highest level. This method can inparticular also be used in combination with the method explained abovein which trapping instructions from lower levels have priority relativeto trapping instructions from higher levels, whereby this “switch” inthe highest level breaks this priority rule. A priority instructionaccording to the fifth aspect of the invention can in particular beprovided corresponding to this.

In the trapping methods of the different aspects explained above themethod is typically controlled by means of trapping parameters andtrapping instructions. In this method of the different aspect it isappropriate to provide a set of specification values (trappingparameters and trapping instructions) in the printing apparatus or inits print data controller, according to which specification values thetrapping method can be controlled. Since the trapping method is verymuch determined by the quality of the printing apparatus, it isappropriate to provide a complete set of such specification values, suchthat in practice print data are to be transmitted to the printingapparatus with quite a few further parameters and trapping instructionsthat individually match the trapping method to the respective printdata.

All aforementioned aspects are in particular advantageously usable inconnection with the aforementioned data streams Advanced FunctionPresentation (AFP) and the data streams derived therefrom (such as, forexample, MO:DCA or IPDS), which are subsequently also called AFP/IPDSdata streams.

The pixel file can be a bitmap file designed in the classical sense, inwhich only a one-bit item of information is provided regarding eachpixel. However, it can also be a bitmap in which each pixel is encodedin a plurality of bits, for example 4 or 8 bits, in particular in aper-byte encoding. For example, various grey values (for example 2⁴=16or 2⁸=256 grey values) can thereby be stored with regard to each pixel.Both types of pixel file are viewed as bitmaps in the scope of thepresent specification.

In the cited aspects of the preferred embodiment in particular a hostcomputer or a print server can be provided for transfer of the documentdata streams between a data processing system generating the documentdata stream and a data processing system (as a generating dataprocessing system) processing the document data stream. The processingdata processing system can in particular be designed as a print server,as a computer with a parsing unit and/or as a raster processor and inparticular as a print data controller integrated into a printingapparatus or connected to this. Given the output of the data by a hostcomputer to a print data controller integrated into a printing apparatusvia one of the cited systems (such as, for example, a print server),this system can in particular convert the data, for example from theMO:DCA format into the IPDS format.

Fundamental Principle of the Method

A fundamental principle of trapping is simple and already known fromdiverse trapping methods: the lighter colorant is slightly expanded inthe region that should be occupied by the darker colorant. The lightercolorant is obscured by the darker colorant and should no longer berecognizable. The darker colorant or, respectively, the darker color isdeterminative for the contour of the object.

The method of the preferred embodiment for trapping of print data with aplurality of different objects is subsequently explained using FIGS. 1 athrough 1 c and 2 a through 2 c.

Essentially, the print data exist in a format in which individualobjects are defined. These are normally a plurality of objects. Theprint data thus normally comprise objects in vector representation andother predetermined objects before the trapping. With the insertion ofthe trapping regions the print data are simultaneously rastered into abitmap file. In the present method this occurs in that the print datacomprising a plurality of objects and a bitmap file into which the printdata are to be transferred are simultaneously provided. The objects areindividually transferred into the bitmap file. FIG. 1 a shows arectangle 1 that is contained in a bitmap file and is filled with acolor with a predetermined brightness. Furthermore, FIG. 1 shows adiagonally-running bar 2 that is an object 3 of the print data. This barshould be inserted into the rectangle 1 such that it extends from thelower left corner of the rectangle 1 to the upper right corner. The bar2 is lighter than the rectangle 1. The bar 2 is a component of the printdata and is depicted in this as a vector object. The bar 2 is thus anobject. The rectangle is represented by pixels in the bitmap file. It istherefore not an object.

In the rectangle 1 contained in the bitmap file the region 4 in whichthe bar 2 should be inserted is initially punched out (knocked out)(FIG. 1 b). It is hereby avoided that there is a large-area overlap ofthe colors of the rectangle 1 and of the bar 2, whereby the color of thebar 2 is enforced true to the original. Since the bar is lighter thanthe rectangle 1, the knocked-out region 4 corresponds exactly to thesize of the bar 2.

The object 3 in the form of the bar 2 is subsequently inserted into theknocked-out region 4 in the bitmap file. The object 3 is hereby rasteredinto pixels that are entered at the corresponding points in the bitmapfile. Since the object 3 is lighter than the adjoining rectangle 1, thebar 2 in the bitmap file is respectively expanded at the edges by atrapping region or, respectively, an overfill (which extends beyond theknocked-out region 4) to the dark section of the bitmap file. Thecontour of the bar 2 is demarcated by the darker color of the rectangle1 that is cut out exactly in the shape of the bar.

Upon rastering of the object 3 the trapping regions or, respectively,overfills 5 (calculated in advance using the object) have been added.

In the image with the bar 2 crossing the rectangle 1 (shown in FIG. 1),a circle 6 should now be inserted in the center of the rectangle 1. Thecircle 6 is filled with a color whose brightness lies between that ofthe rectangle 1 and the bar 2.

The diameter of the circle 6 is greater than the width of the bar 2,such that the circle extends on both sides beyond the bar 2 into theregion of the rectangle 1. Upon knocking out the region 4 for the circlethe edge 7 of the circle (which edge 7 abuts on the region of therectangle 1) is knocked out with exactly the size of the circle,contrary to which the edge 8 of the circle that adjoins the lighter bar2 is knocked out with a somewhat reduced size. The bar 2 hereby extendsinto the region of the circle 6. This region extending into the regionof the circle 6 forms an overfill 5 (FIG. 2 b).

The circle itself (which forms an object 3 in the print data) issubsequently inserted into the knocked-out region 4 in the bitmap file.The circle 6 is hereby rastered into pixels that are entered into thebitmap file at the corresponding points. Since the circle 6 is lighterthan the region of the rectangle 1, the edge 7 of the circle 6 whichadjoins the region of the rectangle 1 is expanded by an overfill 5 thatextends into the region of the rectangle 1. Here the contour of thecircle is defined by the edge of the dark color of the rectangle 1.

At the edge 8 of the circle 6 that adjoins the bar 2, the circle isinserted into the bitmap file with exactly its own size since here thedarker (relative to the bar 2) color of the circle 6 defines the contourof the circle.

Using two objects (bar 2, circle 6) the insertion of the same into thebitmap file is explained above. The objects are hereby individuallyinserted into the bitmap file, whereby the trapping regions or,respectively, overfills 5 are calculated at the objects themselves andthe knocking-out and insertion of the objects occurs corresponding tothe determined overfills. Upon insertion of the objects these arerastered in the bitmap file.

A preferred embodiment was explained above using objects that are filledwith a color of predetermined brightness. The expression “color” washereby used in a simplified manner. In multi-color printing a color isnormally comprised of a plurality of colorants (dyes) that aresuperimposed in different ratios as needed. The individual colorants aredealt with in separate color separations by the control programs. Allcolor separations are superimposed to generate an overall image. Given amulti-color printing the knocking out occurs throughout all colorseparations (planes), contrary to which the overfills are determined andinserted separately for the individual color separations.

In FIG. 3 a printing system is shown with which color image data aregenerated in a user software program 10 running on a user computer 9.The image data so generated are supplied to a print server 11 as printdata. These print data exist in a print data language such as, forexample, AFP, PostScript, PDF or PCL. The print server 11 is connectedto a network 12 (such as, for example, the Internet) and can receiveprint data from different user computers.

The print server 11 is connected with a printing apparatus 13. Onlythree printing stations 14, 15, 16 are shown in FIG. 3. A printingapparatus for printing with a highlight color color requires only twoprinting stations, three printing stations for printing with twohighlight color colors and four to six printing stations for printing ina full color space (YMCK). Each printing station comprises a developerstation 14 a, 15 a, 16 a, an exposure unit 14 b, 15 b, 16 b (such as,for example, a light-emitting diode comb) and further knownelectrophotographic components such as a photoconductor drum and acorotron device.

The data received from the print server 11 are received by a scalableraster architecture (SRA) print data controller 17 contained in theprinting apparatus 13. In the print data controller 17 the trappingmethod is executed in real time and the print data are rastered intoindividual pixels and supplied in a color precise manner to the printinggroups 14, 15, 16 or, respectively, the corresponding light-emittingdiode combs 14 b, 15 b, 16 b to form a latent image on the correspondingphotoconductor drum. The electrostatic images so created are thenelectrophotographically developed with toner in a known manner andprinted on a recording medium 18 (which here comprises individual papersheets).

The raster process in the print data controller can additionallycomprise a screening process in which the rastered pixels are preparedin a machine-specific manner before they are output to the light combs14 b, 15 b, 16 b. The screening process can be executed downstream fromthe trapping process or also in a step with the trapping process or,respectively, the raster process. The execution in a common step is inparticular possible given 1-bit print data (what are known as bi-levelprint data); the execution in separate steps is normally preferred givenprint data that are encoded in a plurality of bits (grey level data,what are known as multi-level print data).

The method workflow of the method for trapping and rastering of theprint data that is executed in the print data controller 17 issubsequently explained in detail using the flow charts shown in FIGS. 4and 5. The method initially starts with the step S1 (FIG. 4). In step S2a single object is extracted from the print data, which single objectshould be inserted into a bitmap file at the corresponding point atwhich it is located in the print data.

In step S3 trap regions or overfills of the object are calculatedrelative to the color regions or grey level regions present andadjoining the object in the bitmap file. The rules according to whichthe overfills are calculated are explained in detail further below.

In step S4 the object is inserted into the bitmap file, whereby theobject is rastered into pixels and the individual pixels are insertedinto the bitmap file.

Subsequently it is checked whether a further object is present that isto be inserted into the bitmap file (step S5). In the event that afurther object is present, the method workflow passes to the step S2.Otherwise the method ends with the step S6. The objects are thusindividually transferred into the bitmap file with the present method.Using the object the overfills are hereby calculated in relation to thebrightness of the color regions of the bitmap file adjoining the object.This has the advantage that the complete information of the objects isavailable without the production of additional tables or lists of theshapes of the objects. Since the overfills are generated upon knockingout or rastering in the bitmap file, it is not necessary to generateadditional objects at the object level for the overfills. Thedetermination of the overfills using the individual objects with regardto the bitmap file and the insertion of the overfills into the bitmapfile can thus be executed in the print data controller 17 of theprinting apparatus 13 without delay of the printing procedure.

The insertion of an object into the bitmap file (step S4) is depicted inthe flow chart shown in FIG. 5. This method workflow begins with thestep S7. In step S8 a region for insertion of the respective object iscut out or, respectively, knocked out in the bitmap file. Overfills thatprotrude into the region of the object are hereby to be taken intoaccount. For example, such overfills occur when the object to beinserted is darker than the adjoining color region of the bitmap file.The excision can also be omitted in specific applications (for exampleoverprint).

In the subsequent step the object is rastered into the bitmap file,whereby here overfills that extend the object into the adjoining regionsof the bitmap file are to be taken into account. This is, for example,the case when the object is lighter than the adjoining regions of thebitmap file.

This method workflow is ended with step S10.

Trapping Rules

In the present method the neutral density of the respective colorant orof the respective color can be used to decide which colorant or whichcolor is lighter. In the CMYK color space the neutral density ND for acolorant is defined by the following formula:

ND=−1.7·log(1−c·(1−10^(−0.6d))),

whereby d is the specific neutral density of the respective colorant(which for the most part amounts to 0.61 for cyan, 0.76 for magenta,0.16 for yellow and 1.70 for black. c is the concentration of thecolorant or of the coloring agent with which this is applied on therecording medium. The concentration comprises a value range from 0 to 1.c is also designated as a degree of coverage.

The neutral density ND for a color results from the sum of the neutraldensities of the individual colorants as follows:

ND=(ND _(C) +ND _(M) +ND _(Y) +ND _(K))

In the present method three types of overfills or traps are to bedifferentiated: a SPREAD is an overfill in which the lighter color orthe lighter colorant is expanded into the darker color or the darkercolorant.

A CHOKE is an overfill in which the darker color region is locatedwithin a lighter color region, whereby the lighter color region isknocked out in the region of the darker color region so that the darkercolor region is reproduced in an optimally color-fast manner. Theoverfill of the CHOKE is hereby executed in that the knocked-out regionof the lighter color region is reduced, whereby the lighter color regionis again expanded into the darker color region.

There is also the case that two different colors or two differentcolorants that, in spite of their color differences, exhibit the sameneutral density are present in two adjoining regions. The overfillhereby used is called CENTER or CENTER-TRAP, and it is symmetricallyarranged around the boundary line between the two adjoining surfaces.The original contour is hereby maintained. However, such a CENTERoverfill is not applied for black or non-transparent or opaque colors oropaque colorants. Given black and other opaque colors, the adjoiningcolors or colorants are always expanded below the black or the otheropaque colors.

Different trapping rules are applied dependent on the respective type ofthe colorant or type of the color. Given translucent colors (that aresubsequently also designated as “normal colors”), all trapping rules areapplied. This also occurs for the typically employed process colorscyan, magenta and yellow that are translucent.

Transparent colors, in particular transparent lacquers, are in principlenot trapped.

Non-transparent colors are handled like black, meaning that the sametrapping rules as for black are applied, according to which theadjoining colorants and colors are expanded below the opaque color.

Special spot colors (such as, for example, gold or silver) that lieoutside of the gamut of the employed color space are ignored intrapping. Spot colors are also designated as highlight color colors.

In an image data file there are many objects that adjoin one another. Sothat too many overfills are not generated that in their entirety cannegatively influence the image, the difference of the neutral density ofadjoining regions is calculated. An overfill is generated only when thedifference amount lies above a predetermined magnitude. This thresholdtypically lies in the range from 0 to 50% and advantageously in therange from 5% to 40% of the degree of coverage with which the colorantis applied on the recording medium. In the framework of the preferredembodiment it is also possible to employ a threshold using thedifference of the degree of coverage or the luminance of the adjacentcolor surfaces instead of the neutral density. Given multi-colorprinting this threshold is applied for every single colorant.

In principle it applies that, the greater the threshold, the feweroverfills are generated. Therefore in practice a threshold of at least20% to 50% has proven to be very worthwhile.

Individual determined objects are treated with different trapping rules.

Graphic objects are objects defined by means of vectors that are for themost part filled with a monochrome color. Given two such adjoiningobjects it is simple to decide whether an overfill or no overfill is tobe executed. It is more difficult when the graphic objects are developedin a color curve. This is explained in detail below.

In principle letter objects are treated like graphic objects. However,given small letter objects whose stroke width lies below a predeterminedlimit width, given trapping problems occur, whereby the trapping worsensthe readability of the letters. The width of the letter objects istherefore compared with the maximum overfill width. In the event thatthe overfill width of the letter object is smaller than twice themaximum overfill width, the overfill width is reduced by a specificamount (for example by 50%). In the event that the width of the objectis still smaller than twice the reduced maximum overfill width, notrapping is executed; rather, the letter objects are printed asoverprint, meaning that they are printed on the background color withoutthe background color being knocked out in the region of the letterobjects. No knock-out (cutting) is thus executed.

Black objects are treated like non-transparent objects, such that allother colors or colorants are expanded below these objects. All objectswhose neutral density lies above a specific threshold are treated asblack objects. This threshold lies in the range from 70% to 100% of theneutral density of black. It advantageously lies in the range from 85%to 95% of the neutral density of black. In principle highlight colorcolors can be viewed as black.

From offset printing it is known to generate a “superblack”. Givenelectrophotographic printers that print with toner particles, it can beappropriate to print other colors below the black to increase its colordensity in order to obtain an intensive black. These other colors aredesignated as support colors. So that a mis-registration is not visiblehere, these support colors that are printed below the black colorantsare trapped in reverse, meaning that they are retracted a bit at theborder region. It is hereby securely prevented that the support colorsare completely colored by the black colorant given a mis-positioning A.

Highlight color objects are objects that comprise a single, specificcolorant. The highlight color normally generates a color impression thatcorresponds to a mix of a plurality of colorants and often lies outsideof the gamut that can be achieved with the process colorant. Thehighlight color color is not mixed with other process colors.

Since the degree of coverage of the highlight color color cannot becompared with the degree of coverage of a color composed of a pluralityof process colors, given calculation of the trapping threshold thedegree of coverage is not used; rather, the neutral density of theobject is used.

Image objects themselves are normally subjected to no trapping method.Image objects are trapped against further adjoining objects at theiredges. Here there are four different possibilities in principle: givencenter trapping both the image and the adjoining vector objects areexpanded. Given neutral trapping each pixel is compared with the neutraldensity of the adjoining vector object and the overfill is executedpixel-by-pixel at one side or the other side. However, this can resultin a diffuse edge impression, which is not desirable.

Given dark images a choke image trapping is executed, meaning that theadjoining vector object is expanded below the image. Contrary to this,given light images a spread image trapping is executed, meaning that theimage is expanded over the object region.

The preferred trapping rule for image objects is the center trapping,which is predetermined as a standard rule (DEFAULT). Grey level imagesare treated like color images. No trapping is executed between adjoiningimage objects.

Since the trapping is executed wholly automatically in the presentmethod, certain trapping parameters are to be provided. These trappingparameters can be specification values (default values) stored in theprinting system or also be added trapping parameters individual to theprint document. A set of complete trapping parameters in the printingapparatus 13 or in its print data controller 17 is advantageously storedsuch that print data can be trapped in the printing system solely withthe trapping instruction that a trapping should be executed. Thiscomplete set of trapping parameters (default values) can be overwrittenor replaced by individual trapping parameters transmitted with the printdata stream, or the resources explained further below, which resourcescan also be stored in the printing system, can also be replaced by thesedefault values.

In the present method two different sets of trapping parameters areadvantageously used, whereby the one set of trapping parameters controlsthe trapping parallel with the transport direction of the recordingmedium in the printer and the other set of trapping parameters controlsthe trapping transverse to the transport direction of the recordingmedium in the printing device.

The individual trapping parameters are subsequently explained using thetables shown in FIG. 6.

The width of the overfill (trap) is advantageously predetermined in afixed manner. This significantly simplifies the generation of overfillssince it must merely be determined whether an overfill should begenerated and at which side of the boundary surface between twoadjoining objects it should be provided, or whether it should bearranged centered around the boundary line. The width of the overfillnormally amounts to one or two pixels. Given a resolution of 600 dpi,two pixels corresponds to approximately 1.5 mm [sic]. For testingpurposes it can be advantageous to set the width of the overfill to afew millimeters since the overfills can hereby be detected immediatelyin the print image.

For non-black colorants the width of the overfills normally amounts to0.02 to 5.0 mm, whereby the same values can be used for the X-directionand Y-direction (table 1).

The width of the overfills for black or opaque colorants is normallytwice as large as the width of the overfills for non-black colorants(table 2).

If print data are scaled, i.e. transferred to a larger or smaller scale,the overfills are maintained with unchanged width. A scaling of thewidth of the overfills is not advantageous.

Any direction of a normal line on the boundary line between two colorsurfaces that runs either vertically or in a region between a verticaland a line angled by 45° relative to the vertical is viewed as anx-direction in the determination of the width of the overfill. The widthof the overfill is then set by the boundary line in the direction of thevertical and not in the direction of the normal relative to the boundaryline. In a corresponding manner, any direction between a horizontal anda line angled by 45° relative to the horizontal (or, respectively,between a horizontal and a horizontally running normal) applies as aY-direction of a normal situated on a boundary line. The width of thetraps is also set here not in the direction of the boundary line butrather in the direction of the horizontal (Y-direction).

In practice this means that the overfill amounts to one or two pixelseither in the direction of the vertical (X-direction) or in thedirection of the horizontal (Y-direction). Therefore no elaboratecalculations of the width of the overfills are necessary and theoverfills can be entered into the bitmap file without largecomputational effort. This simplifies the trapping method on the fly inthe printing method.

Table 3 indicates the rules for the difference amount for assessment ofthe brightnesses of two adjacent regions. When the difference of thebrightnesses of two adjoining regions is less than the different amount,no overfills are generated. In multi-color space (CMYK) each colorant ofthe object is compared. The lighter colorant is multiplied with therespective degree of coverage and increased by the percentile differenceamount, and no trapping is necessary in the event that the lightercolorant thus increased is darker than the darker colorant multipliedwith its degree of coverage. This comparison is executed between allcolorants of the adjoining regions. When a comparison yields thenecessity of a trapping, a trapping is thus executed.

Colors with a neutral density above a predetermined density limit (blackdensity limit) are treated like black. The default value lies at 100%(table 4). However, in some cases it can also be appropriate to lowerthe density limit, for example to a range from 80% to 95%.

The table 5 shows the black-color limit that indicates as of whichdegree of coverage the color black is to be assessed as black and not asa grey color tone. The default value lies at 1.0. However, other valuesbetween 0.85 and 1 (in particular between 0.85 and 0.95) are alsoreasonable.

Small black objects such as letters or lines are often better printedthan other objects without their region being knocked out. Thisoverprinting requires significantly less computer power than aknocking-out and generation of an overfill. An overprint is normallymade when the text is smaller than a predetermined size (12 pt) or linesare smaller than the width of the overfill for black color. Thecorresponding ranges of the limit values are specified in table 6.

A center trap is normally generated only when the neutral density of thetwo adjoining regions is the same. The range within which a center trapis generated can be expanded with a center trap limit. The center traplimit comprises the range from 0.0 to 1.0 (table 7). The center traplimit is applied in that the neutral density of the darker color ismultiplied with the center trap limit, and a center trap is generated inthe event that the product is smaller than the neutral density of thelighter color.

The table 8 shows some shapes of the overfills, normal overfills forspread and choke that are also clipped (meaning that the overfill thatextends into the adjoining color region does not extend beyond thisadjoining color region at the edge) Overfills with beveling, a roundingand mitering are also shown.

Given mitering the problem exists that given small angles an overfillwith a very narrow, long point arises. It is proposed to truncate amiter overfill when it extends beyond the respective width of theoverfill in the X-direction or in the Y-direction in the region of thepoint. This is shown in FIGS. 7 a and 7 b using two examples. Thislimitation of the miter point incurs almost no computational effort; itis independent of the orientation of the miter angle. It can bedetermined very quickly and does not delay the calculation of theoverfills. The method can therewith be executed quickly without largecomputation effort and in a resource-saving manner.

When two regions whose brightnesses gradually change abut one another,it can thus be that on a boundary line the one boundary surface at onesegment and the other boundary surface at another segment is lighterrelative to the respective other boundary surface. This leads to thesituation that the overfill extends into the one region at the onesegment and into the other region at the other segment. This change canbe executed precipitously or a more gradual transition can also occur. Asliding trap limit that comprises a number range from 0.0 to 1.0 isprovided for adjustment of this transition. If the value of the slidingtrap limit is 1.0, the transition between the two overfills thus occurssuddenly (FIG. 8 a). Given smaller values of the sliding trap limit theoverfill shifts gradually over the boundary line of the abutting colorregions. FIG. 8 b shows a gradual transition for a sliding trap limit ofapproximately 0.5.

To reduce the visibility of an overfill, this can be scaled (trap colorscaling). In the region of the overfill the degree of coverage isreduced by a scaling factor. The scaling factor can adopt values in anumber range from 0.0 to 1.0. It is also possible that different scalingfactors are provided for different colorants. The default value of thescaling factors is 1.0. A scaling factor of 1.0 means that the overfillalways exhibits the degree of coverage of the darker colorant, contraryto which a scaling factor of 0.0 means that the overfill always exhibitsthe degree of coverage of the lighter colorant. This scaling factor isapplied to the difference of the degree of coverage of the darker andlighter colorants and added to the degree of coverage of the lightercolorants. It can herewith be prevented that the overfills are too darkor too light.

Implementation of the Method for Trapping of Print Data in an AFP/IPDSData Stream

The IPDS print data is explained in detail in the IBM publication“Intelligent Printer Data Stream, Reference” S544-3417-06, 7th edition(November 2002). In this publication a diagram is presented on page 31,which diagram is shown in the attachment as FIG. 9. This diagram showsan example of the hierarchical structure of an IPDS print data streamwith a plurality of what are known as presentation spaces. Thesepresentation spaces respectively define a specific region in thedocument to be printed. A plurality of presentation spaces can besuperimposed on one another.

A medium presentation space 18 that defines the print data medium or theprint medium forms the highest level in the hierarchy of thepresentation spaces. This medium presentation space is a limited addressspace in the print data stream that is mapped to a complete page of theprint data medium. There is thus only a single medium presentation spaceon one page of a print data medium. The print instructions and printdata contained in a medium presentation space thus apply for the entirepage.

Furthermore, there is a medium overlay presentation space 19, a pagepresentation space 20, page overlay presentation space 21, object areapresentation space 22 and data object presentation space 23.

All presentation spaces can comprise print data and print instructions.The data object presentation spaces 23 in which the data objects(graphics and text) to be printed are contained represent the lowestlevel of the presentation spaces. These data object presentation spaces23 are linked (merged) with the object area presentation spaces 22 thatare provided for specific objects. The object area presentation spaces22 are in turn linked with page overlay presentation spaces 21. Inprinciple overlays can comprise any arbitrary combination of text, imagegraphic, barcode and what are known as object container data. Overlaysare normally used as a type of form into which the data objects of thelower levels are inserted.

The order in which the individual presentation spaces are linked withone another is exactly established.

In principle, trapping instructions of a lower level have priority overtrapping instructions with regard to a higher level since the printinstructions in a lower level have a more direct relation to therespective object.

In the highest level (the medium overlay presentation space 19) atrapping instruction “global trapping enabling/disabling information” isprovided with which the trapping of the print data stream can begenerally activated and deactivated. This trapping instruction breaksthe priority rule explained above according to which the trappinginstructions of lower levels have priority over trapping instructions ofhigher levels. In principle it allows an operator of the printing systemto activate or deactivate the trapping in a simple manner in that thistrapping instruction is merely inserted into the uppermost level.

The trapping instructions can be defined separately with a trappingtriplet (which is explained in detail further below) in eachpresentation space. The trapping settings in the individual presentationspaces can hereby be individually regulated. In principle it alsoapplies here that the trapping instructions of one presentation space ofa lower level can overwrite (overrule) a corresponding trappinginstruction of a presentation space of a higher level. Deviating fromthe typical practice of the IPDS data stream, the trapping can hereby becontrolled in the lower levels (for example the data object presentationspaces) and this trapping instruction cannot be modified by presentationspaces provided in higher levels. A user who generates a data object tobe printed can hereby unambiguously and irrevocably designate whetherand how this data object is subject to the trapping method. There aredata objects in print data that generally may never be subjected to atrapping method. Such data objects are, for example, barcodes. Ifbarcodes were subjected to a trapping method, the stroke width of theindividual barcode would be altered, whereby the meaning of the barcodewould be lost. Even if a trapping should be provided at presentationspaces arranged in higher levels, data objects in which the trappingmethod is enabled at the level of the data object presentation spacesare not subject to a trapping method.

Not all trapping parameters must be defined in the print data stream.Trapping parameters not defined in the print data stream aresupplemented by default values stored in the printing apparatus 13 or,respectively, in the print data controller 17. In practice it isappropriate to establish optimally few trapping parameters in the printdata stream since the trapping method is very printer-specific. Theoffset of the individual color separations on a print data mediumnormally depends on the mechanical properties of the printing apparatus,such that in principle trapping parameters (such as, for example, thewidth of an overfill) are best established in the printing apparatus 13.Only trapping parameters that are not specific to the print data itself(such as, for example, the deactivation of the trapping method forbarcode objects) should be defined in the print data stream.

The principle of the supplementation of the trapping parameters withspecification values in the printing apparatus allows the generation ofthe print data stream to be kept simple since only a few fundamental andgeneral trapping parameters are defined in the print data stream, whichfundamental and general trapping parameters are supplemented by furtherspecific trapping parameters in the printing apparatus.

According to the preferred embodiment, the resource structure of the AFPdata stream and of the IPDS data stream is used for the control of thetrapping method. Print data are generated at the user computer 9 (FIG.3) and transmitted to a print server 11 by means of the AFP data stream.In the print server 11 the AFP data stream is prepared and convertedinto an IPDS data stream for output to the printing apparatus 13. In theprint server 11 a plurality of processes run that are controlled bysoftware modules. A first software module embeds resource data (such asfonts or overlays) that are called in the original print data streaminto said print data stream. A second software module, the parsingmodule, checks the print data stream for consistency with predeterminedrules. A pre-parsing process that is implemented by a correspondingsoftware module is upstream of the parsing process, in which pre-parsingprocess an identification datum (in addition to the resource name) isassociated with each resource call and the associated resource file, viawhich identification datum the resource is uniquely identified relativeto all other resources of the document data stream. Within the documentdata stream the resource can then be called once or multiple times bymeans of the resource name and/or the identification datum forpresentation of the print data and the resource data at the printingapparatus 13. The processes shown here in the print server can also beimplemented in part or entirety in the print data controller 17 of theprinting apparatus 13.

In the shown exemplary embodiment the AFP document data stream comprisesdocuments that correspond to the MO:DCA standard and that respectivelycomprise reference data regarding data objects that are available viathe print server 11 and in the print data controller 17. The resourcedata can thereby be transferred from the user computer 9 to the printserver 11 and the print data controller 17 separate from the MO:DCAdocument data stream or can already be stored in the print server 11 andin the print data controller 17 as external resources. However, theresource data can also be transferred as embedded resource data (whatare known as inline resources) together with the document data streamfrom the user computer 9 to the print server 11. Further details of acorresponding data processing are described in WO-A1-2004/0008379, whichfor this is incorporated by reference at this point of thespecification. The resource data can comprise what are known as dataobject resources that contain object data which are in particularreferenced multiple times in an identical manner in the document datastream. Such data objects can, for example, be image data, text data,graphic data and/or trapping data. The reference to the object resourcescan occur via an object resource library that comprises identifying dataregarding the object as well as data bout the storage location of thecorresponding object data. The library comprises a data object resourceaccess table (RAT) that, for the print server 11, acts as an index tablefor the access of the print server to the resource data.

The print server 11 receives the MO:DCA document data stream from theuser computer 9, converts it into an IPDS document data stream and sendsthis to the printing apparatus 13. In the course of the data conversionit reads the reference information (name) of a data object from theMO:DCA document data stream and accesses the stored data resource withthe aid of the data object resource access table (RAT). The completedata of the object are then integrated into the IPDS data stream andsent to the printing apparatus 13. This method can be applied just aswell when the data are sent to another output apparatus (for example toa color monitor) instead of to a printing apparatus.

An MO:DCA document data stream is structured in data elements that arelargely self-explanatory. Structured fields are important components ofthe MO:DCA structure. A structured field is subdivided into a pluralityof parts. A first part (introducer) identifies the desired command,specifies the complete length of the command and specifies additionalcontrol information (for example whether additional padding bytes arepresent). The data contained in a structured field can be encoded asfixing parameters, comprise repetition information (repeating groups),keywords and what are known as triplets. The fixing parameters deploytheir effect only for the structure in which they are contained.Repetition groups specify a grouping of parameters that can occurmultiple times. Keywords are self-explanatory parameters that typicallycomprise two bytes, whereby the first byte is an identification byte forthe keyword and the second byte is a data value characterizing thekeyword. Triplets are self-explanatory parameters that comprise, alength specification in a first byte, an identification informationcharacterizing the triplet in a second byte and then up to 252 databytes. The cited data structures of an MO:DCA document data streamdefine a syntax that can be evaluated in the course of a parsing processand is flexibly expandable.

MO:DCA data streams are hierarchically subdivided similar to the IPDSdata streams explained above.

The resource data can be generated at different points: the usercomputer 9, the print server 11 and even by means of a control panel onthe printing apparatus 13. These resource data are sent once to theprint data controller 17 of the printing apparatus 13 and stored thereso that they can always be used again when a corresponding print datastream references them.

For a user of the user computer 9 or operator of the print server 11 thepossibility hereby exists to generate specific trapping settings once asresource data and to store them at the print data controller 17, whichspecific trapping settings are then repeatedly called.

Some trapping examples in an IPDS print data stream are subsequentlyexplained:

FIG. 10 shows an example in which two presentation spaces 24 are filledwith respectively one uniform dark background color and with apresentation space 25 lying beneath them that is filled with a lightercolor. Here overfills are to be generated at the edge of thepresentation spaces 24 since here color regions of different brightnessabut one another. A trapping instruction in the presentation space 24regulates the manner of how the trapping is executed at the edge withpresentation space 25.

Shown in FIG. 11 is a similar example with two presentation spaces 24 inwhich a circular element (data object presentation space 26) isrespectively arranged. The upper presentation space 24 is transparent,i.e. filled with no background color. This presentation space 24comprises an instruction that the trapping of objects contained thereinwith underlying presentation spaces is to be implemented.

Contrarily, the lower presentation space 2 is filled with an opaquebackground color, such that the circular element 26 is to be trappedwith regard to the presentation space 24 and not with regard to theunderlying presentation space 25.

It can also be desirable to employ different trapping rules fordifferent elements within a presentation space, for example fordifferent graphic elements (GOCA) that possess filled or empty borders.“Trapping Drawing Orders” and “Trapping Text Controls” are provided forsuch cases.

In principle no trapping is executed given multi-level images containedin IOCA presentation spaces since they are considered as opaque objects.Here a trapping occurs only at the borders of the image or,respectively, at the edges of the IOCA presentation space when this isfilled with a background color (FIG. 12).

FIG. 13 shows the AFP/IPDS trapping parameter triplets in table form,whereby the triplet (offset, name, range) is specified in the respectivefirst three columns. The meaning of the triplet is explained in thefourth column. In the fifth column it is specified whether the tripletsare optional or mandatory. Exceptions are specified in the sixth column.

The trapping is conventionally dependent on the paper run direction. Thetrapping parameters in the paper run direction therefore often differfrom those transverse to the paper run direction. Given the trappingparameter triplets the Y-direction always means parallel to the paperrun direction and the X-direction is rotated by 90° transverse to thepaper run direction. In the event that an object is rotated, the printdata controller automatically applies the parameter of the correspondingdirection.

Typically an L-unit is defined as a unit of measurement in an IPDS datastream. This L-unit can be defined divergently for the trappingparameters. Some abbreviations are listed in the tables. They mean:

TID Trapping ID UPUB L-units per UnitBase TS Limit trap step limit(difference amount) BD Limit black density limit (density limit) BCLimit black color limit CT Limit center trap limit TCS trap colorscaling (scaling factor)

The trapping method is primarily executed in real time in the print datacontroller 17 (FIG. 3), such that the print data are supplied withoutdelay in the printing process. The print data controller 17 does notnecessarily have to be integrated into the printing apparatus 13, butrather can also be arranged outside of the printing apparatus 13, forexample as a separate raster image process (RIP). The print datacontroller 12 can comprise special hardware circuits, for example FPGAs(Free Programmable Gate Arrays) or ASICs (Application SpecificIntegrated Circuits). It can also be operated on a typical computer(data processing apparatus) such as, for example, a personal computerwith one or more Intel® Pentium Processors or another processor systemwith suitable operating system. It can furthermore be provided with amicroprocessor in which is stored an executable computer program that isdesigned for execution of the method. This computer program cannaturally also be stored on a data medium independent of the printingsystem.

The preferred embodiment is in particular suitable to be realized as acomputer program (software). As a computer program module it cantherewith be distributed as a file on a data medium such as a disketteor CD-ROM or as a file via a data or communication network. Such andcomparable computer program products or computer program elements arevariations of the preferred embodiment. The workflow of the preferredembodiment can be applied in a computer, in a printing apparatus or in aprinting system with upstream or downstream data processing apparatuses.It is thereby clear that corresponding computers on which the preferredembodiment is applied can comprise further known technical devices suchas input means (keyboard, mouse, touchscreen), a microprocessor, a dataor, respectively, control bus, a display device (monitor, display) aswell as a working memory, a fixed disk storage and a network card.

While a preferred embodiment has been illustrated and described indetail in the drawings and foregoing description, the same is to beconsidered as illustrative and not restrictive in character, it beingunderstood that only the preferred embodiment has been shown anddescribed and that all changes and modifications that come within thespirit of the invention both now or in the future are desired to beprotected.

1-39. (canceled)
 40. A method for trapping of generated print data witha plurality of objects, comprising the steps of: generating the printdata together with trapping instructions in a print data stream forexecution of the trapping; transferring the print data stream to a printdata processing apparatus; and referencing with the print data streamresource data that comprise at least one of trapping parameters or thetrapping instructions.
 41. A method according to claim 40 wherein theresource data are stored in the print data processing apparatus.
 42. Amethod according to claim 40 wherein the print data stream is anAFP/IPDS data stream.
 43. A method according to claim 42 wherein theprint data stream comprises AFP/IPDS trapping triplets that containtrapping instructions.
 44. A method according to claim 40 wherein theprint data are transferred in a print data stream together with thetrapping instructions, and the print data stream is structured indifferent levels, whereby a higher the level a greater the scope inwhich the instructions contained in the respective level act, andtrapping instructions from lower levels having priority relative totrapping instructions from higher levels.
 45. A method according toclaim 44 wherein a trapping instruction with which the trapping in anentire scope of the highest level can be activated or deactivated isprovided in the highest level.
 46. A method according to claim 44wherein print instructions are inherited from the higher levels to thelower levels.
 47. A method according to claim 44 wherein the trappinginstructions are executed in a print data controller.
 48. A methodaccording to claim 47 wherein the trapping instructions are contained inpresentation spaces contained in the IPDS print data stream, thetrapping instructions regulating the trapping within the respectivepresentation space, the presentation spaces being arranged in differentlevels.
 49. A method according to claim 40 wherein a complete set oftrapping parameters is stored as default values in the print datacontroller.
 50. A method according to claim 40 wherein the objects areindividually transferred into a bitmap file and for this the followingsteps are respectively executed: in the bitmap file, determiningoverfills for the respective object relative to the color regionsabutting the object according to predetermined trapping rules; andinserting the object and the overfills into the bitmap file, and uponinsertion the object and the overfills being rastered into the bitmapfile.
 51. A method according to claim 50 wherein the print data aremaintained as well during the transfer of the individual objects intothe bitmap file.
 52. A method according to claim 50 wherein giveninsertion of the object into the bitmap file, the region into which theobject is to be inserted is knocked out from the bitmap file before theobject is rastered into the bitmap file, whereby the knocked-out regioncan be reduced corresponding to the previously-determined overfills. 53.A method according to claim 52 wherein the regions for the objects to beinserted are knocked out throughout all color separations given amulti-color printing.
 54. A method according to claim 50 wherein theoverfills for the individual color separations are determined andinserted separately given multi-color printing.
 55. A method accordingto claims 50 wherein the overfills of two adjoining color regions arecalculated such that a lighter color or a lighter colorant extends intothe region of a darker color or into the region of a darker colorant.56. A method according to claim 55 wherein a neutral density of thecolors or the colorants are compared to establish which color region islighter.
 57. A method according to claim 40 wherein overfills aredetermined only at borders of one of the respective objects when abrightness of the respective object differs from an adjoining region bya difference amount that is greater than a predetermined threshold. 58.A method according to claim 57 wherein a neutral density, a degree ofcoverage, or luminance is used as the brightness.
 59. A method accordingto claim 57 wherein overfills are determined only at segments of bordersof a respective object when a brightness of the respective objectrelative to a region adjoining this segment of the border differs by apredetermined difference amount.
 60. A method according to claim 57wherein given use of a multi-color space the brightnesses of therespective object are compared with the adjoining regions separately foreach color separation.
 61. A method according to claim 57 wherein atborders of an object presented in a highlight color, an overfill isalways determined independent of a brightness difference relative to theadjoining region.
 62. A method according to claim 57 wherein an objectshown in a highlight color is compared with a neutral density of theadjoining region, whereby a sum of neutral densities of all colorseparations is used for comparison with the object shown in highlightcolor.
 63. A method according to claim 57 wherein the threshold lies inthe range from 0 to 50%.
 64. A method according to claim 50 wherein awidth of the overfill is reduced given letters and lines whose strokewidth lies below a first predetermined limit width.
 65. A methodaccording to claim 64 wherein given graphic objects and letters whosestroke width lies below a second predetermined limit width that issmaller than a first predetermined limit width, no overfills aregenerated and the corresponding regions are not knocked out in thebitmap file.
 66. A method according to claim 50 wherein objects whoseneutral density lies above a determined threshold are treated asnon-transparent objects.
 67. A method according to claim 66 wherein thethreshold lies in the range from 70% to 100% of the neutral density ofblack.
 68. A method according to claim 50 wherein support colors printedbelow a specific colorant in order to increase its color density aretrapped in reverse, in that they are retracted a bit at the borderregion.
 69. A method according to claim 50 wherein for trappingdifferent trapping parameters are applied in a transport direction of arecording medium on which the print data should be printed andtransverse to the transport direction.
 70. A method according to claim50 wherein a width of the overfill is not wider than 5 pixels.
 71. Amethod according to claim 50 wherein a width of the overfills for blackand opaque colorants is greater than a width of the overfills fornon-black and non-opaque colorants.
 72. A method according to claim 70wherein a width of the overfill is set in a direction of verticals or ina direction of horizontals, however not in a direction of normalsrelative to a boundary line between two adjoining color regions.
 73. Amethod according to claim 50 wherein given overfills in a region of anarrow, long point, the point does not extend beyond a width of theoverfill in an X-direction or in a Y-direction with regard to anoutermost point of a non-trapped region.
 74. A method for generation ofa print data stream wherein at least one of print data, trappingparameters, or trapping instructions are generated, comprising the stepsof: integrating the print data in the print data stream; and referencingin the print data stream resource data that contain at least one of thetrapping parameters or the trapping instructions.
 75. A method fortrapping of print data, comprising the steps of: at least one ofgenerating, preparing, or transferring the print data in a print datastream together with trapping instructions, the print data stream beingstructured in different levels; and providing the trapping instructionswith priority rules related to said levels.
 76. A printing system fortrapping of generated print data with a plurality of objects comprising:a print data stream controller, the print data controller executing themethod steps of generating the print data together with trappinginstructions in a print data stream for execution of the trapping,transferring the print data stream to a print data processing apparatus,and referencing with the print data stream resource data that compriseat least one of trapping parameters or the trapping instructions.
 77. Aprinting system according to claim 76 wherein the print data controllercomprises a microprocessor and a computer program.
 78. Acomputer-readable medium comprising a computer program for trapping ofgenerated print data with a plurality of objects, said computer programperforming the steps of: generating the print data together withtrapping instructions in a print data stream for execution of thetrapping; transferring the print data stream to a print data processingapparatus; and referencing with the print data stream resource data thatcomprise at least one of trapping parameters or the trappinginstructions.